These sessions are usually run by very enthusiastic "Round my yellow jumper run" fitness jerks who believe that doing a few practice lengths of the pool first will be of great benefit for when you ditch in the North Atlantic.
The secret is, when these chaps drop the dinghy into the pool and inflate it, slip quietly aboard without anyone noticing. Eventually you will be joined by the rest of the course usually dripping wet and exhausted, at which point you can complain bitterly about their lack of consideration.
Another good ploy is when the girls wear old hostie uniforms for the drill, a couple of smart young pilots can slip the spares on and follow the chattering and dripping females into their changing room.
We only got caught out because my mate had a beard.
